Millions of SSE customers on its standard tariff will see their energy bills jump from 28 April – the firm's hiking electricity prices by 14.9% and keeping gas prices steady, meaning those on a dual fuel tariff face an average 6.9% rise.

The energy giant is the last of the big six suppliers to reveal its pricing intentions, and today's announcement follows similar moves by E.on, EDF, Npower and Scottish Power.

If you're one of the 66% of the population on a standard tariff you're almost certainly already overpaying. Do a comparison with our free Cheap Energy Club to see if you can switch and save £290/year after the hikes come in.

More than 3.8 million SSE customers are on its standard tariff, which account for 91% of its entire customer base.

The move means a typical user on SSE's standard dual-fuel tariff, paying by monthly direct debit and on paperless billing, will pay an average £1,129/year once the hikes hit, up from £1,068/year.

Those who are on a fixed or prepaid tariff won't be affected by today's announcement. SSE has said it's adjusting prepay prices from Saturday 1 April in response to regulator Ofgem's price cap – its prepay gas prices will drop 13% on average, while electricity prices will rise for some and fall for others.

'Now we have a true level playing field – and the picture is grim' founder Martin Lewis said: "We now have a true level playing field for comparison, as SSE is the last of the big six firms to announce its pricing intentions. Five have announced hikes – British Gas is freezing prices until August and will, I suspect, increase prices then.  

"The picture is grim – almost everyone on a standard tariff from the big six, including British Gas, is being ripped off. A typical SSE customer will see their bills jump from £1,068 to £1,129 a year, pretty similar to the rest of the firms after hikes.

"Our Cheap Energy Club shows the cheapest tariff on the market would cost you £834 for exactly the same, and all the cheap deals are one-year fixes, so you're guaranteed no price hikes."

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